Process for producing metallic carbonitride

ABSTRACT

The carbonitrides of metals such as those of Groups IV, V and VI of the Periodic Table are prepared by calcining a precursor obtained by (i) reacting the reaction product of ammonia and the halide of a metal with carbohydrate and/or polyvinyl alcohol, or (ii) reacting the reaction product of carbohydrate and/or polyvinyl alcohol and the halide of a metal with ammonia. The desired metallic carbonitride in the form of finely divided powder having a uniform size and excellent sintering properties can be obtained at low energy consumption.

The present invention relates to a process for producing metalcarbonitrides. More specifically, it relates to a process for producingthe carbonitrides of elements of Groups IV, V and VI of the PeriodicTable of Elements.

The term "the carbonitride of a metal" or "a metallic carbonitride" asused herein means (a) a solid solution of a metallic carbide and ametallic nitride, (b) a mixture of a metallic carbide and a metallicnitride and (c) a mixture of the solid solution (a) and the mixture (b).

Carbonitrides of metals are known and mainly used as an ultra-rigid heatresistant material after sintering. Known methods for producing metalliccarbonitrides are, for example,

(1) a method for mixing powdered metallic carbide and powdered metallicnitride,

(2) a method for calcining the mixture as set forth in (1) above at ahigh temperature,

(3) a method for reacting metallic carbide with nitrogen or ammonia at ahigh temperature,

(4) a method for reacting metallic nitride with methane or carbon at ahigh temperature.

However, there are disadvantages in the above-mentioned methods (1) and(2) that (a) special apparatus for uniformly mixing the powderedmetallic carbide and metallic nitride with each other is required and,also, (b) an extremely large amount of energy is required to separatelycalcine the metallic carbide and the metallic nitride prior to thepreparation of the desired metallic carbonitride. Similarly, there isalso a disadvantage in the above-mentioned methods (3) and (4) that,since the metallic carbide or metallic nitride, which has beenpreviously obtained from the calcination at a high temperature, shouldbe reacted with the nitrogen or carbon source at a high temperature, theenergy consumption becomes large. Furthermore, there is also adisadvantage in each of the above-mentioned conventional methods (1),(2), (3) and (4) that finely divided powder of the desired metalliccarbonitride having a uniform size is difficult to produce.

Accordingly, an object of the present invention is to obviate theabove-mentioned disadvantages of the prior conventional method forproducing the metallic carbonitrides and to provide a process forproducing the carbonitrides of metals in which (i) the desired metalliccarbonitride can be produced at a low energy consumption, (ii) a finelydivided powder of the metallic carbonitride can be produced having auniform size and having excellent sintering properties and (iii) thedesired composition of the metallic carbonitride can be readilycontrolled.

Other objects and advantages of the present invention will be apparentfrom the following description.

In accordance with the present invention, there is provided a processfor producing the carbonitride of a metal comprising the step ofcalcining a precursor obtained by (i) reacting the reaction product ofammonia and the halide of a metal wth at least one member selected fromthe group consisting of carbohydrates and polyvinyl alcohols, or (ii)reacting the reaction product of the halide of a metal and at least onemember selected from the group consisting of carbohydrates and polyvinylalcohols with ammonia.

According to the present invention, since the desired metalliccarbonitride can be produced only by calcining the above-mentionedprecursor, the heat consumption is low. In addition, since the desiredmetallic carbonitride in the form of finely divided uniform shapedpowder is obtained, the sintering properties thereof are excellent.Furthermore, a metallic carbonitride having the desired composition canbe advantageously produced by changing the amount of the carbohydratesand/or polyvinyl alcohols to be used.

Typical examples of the halides of metals used in the present inventionare those of a metal selected from the group consisting of Groups IV, Vand VI of the Periodic Table of Elements. Examples of such metallichalides are the chlorides, the bromides and the iodides of metals, suchas, silicon, titanium, zirconium, hafnium, vanadium, niobium, tantalum,chromium, molybdenum, tungsten and the like. These metallic halides canbe used alone or in any mixture thereof.

The carbohydrates used in the present invention can be monosaccharides,oligosaccharide and polysaccharide. Examples of such carbohydrates areglucose, galactose, arabinose, saccharose, maltose, lactose, starch,cellulose and the like.

The polyvinyl alcohols used in the present invention preferably includethose which are obtained by saponifying from 30 to 100% of the acetylgroups contained in polyvinyl acetate. Although there is no limitationin the polymerization degree of the polyvinyl alcohols, the polyvinylalcohols having a polymerization degree of from 500 to 2000 can bedesirably used in the present invention.

Ammonia can be used, either in the liquid state or in the gaseous state,in the present invention.

The precursor of the metallic carbonitride used in the present inventioncan be produced by

(i) a method for reacting the reaction product of the metallic halideand ammonia with the carbohydrate and/or the polyvinyl alcohol, or

(ii) a method for reacting the reaction product of the metallic halideand the carbohydrate and/or the polyvinyl alcohol with ammonia.

Each of these methods (i) and (ii) will be described hereinbelow.

Method (i)

The metallic halide and ammonia can be reacted in any known manner. Forinstance, a method of gradually adding liquid ammonia to a solution ofsuspension of the metallic halide in an inert organic solvent or amethod of blowing gaseous ammonia through said solution or suspensioncan be utilized. The liquid or gaseous ammonia is preferably added to orblown through the solution or suspension until the reaction of themetallic halide therewith is completed. The reaction temperature isgenerally within the range of from -80° C. to 300° C., preferably from-50° C. to 200° C. The reaction product thus obtained can be reactedwith the carbohydrate and/or the polyvinyl alcohol directly as thereaction mixture or after isolating the desired reaction product fromthe reaction mixture.

There are no special limitations in the method for reacting the reactionproduct of the metallic halide and ammonia with the carbohydrate and/orthe polyvinyl alcohol. For instance, the reaction product of themetallic halide and ammonia can be reacted with the carbohydrate and/orthe polyvinyl alcohol by either adding the carbohydrate and/or thepolyvinyl alcohol or a solution or suspension thereof in an inertorganic solvent to a suspension of the reaction product in an inertorganic solvent or the reaction mixture itself obtained in the previousstep; or vice versa. The reaction temperature is generally within therange of from -50° C. to 150° C. The precursor thus obtained can besubjected to a subsequent calcination step after isolation.

Method (ii)

There are no special limitations in the method for reacting the metallichalide with the carbohydrate and/or the polyvinyl alcohol. For instance,the metallic halide can be reacted with the carbohydrate and/or thepolyvinyl alcohol by either adding the carbohydrate and/or the polyvinylalcohol or a solution or suspension thereof in an inert organic solventto a solution or suspension of the metallic halide in an inert organicsolvent; or vice versa. The reaction temperature is generally within therange of from -50° C. to 150° C. The reaction product can be reactedwith ammonia directly as the reaction mixture or after isolating thedesired reaction product from the reaction mixture.

There are also no special limitations in the method for reacting thereaction product obtained above with ammonia. For instance, the reactionproduct can be reacted with ammonia by gradually adding liquid ammoniato, or blowing gaseous ammonia through, a solution or suspension of thereaction product in an inert organic solvent or the reaction mixtureobtained in the previous step. The reaction temperature is generallywithin the range of from -80° C. to 300° C., preferably from -50° C. to200° C. The precursor thus obtained can be subjected to a subsequentcalcination step after isolation.

In the above-mentioned methods (i) and (ii), each reaction is preferablycarried out, with or without stirring, in the absence of water andoxygen. The inert organic solvent which can be used in theabove-mentioned reactions include, for example, aromatic hydrocarbonssuch as benzene, toluene, xylene; aliphatic hydrocarbons such as hexane,heptane, octane; and halogenated hydrocarbons such as chlorobenzene,chlorotoluene, carbon tetrachloride, methylene chloride.

In the above-mentioned methods (i) and (ii), the carbohydrate and/or thepolyvinyl alcohol are preferably used in an amount within the range ofvalue N defined by the following relationship [I] of from more than 0 toless than 6, more preferably from more than 0 to less than 4.

    N=(a×b)/c                                            [I]

wherein a is the number of hydroxyl groups contained in the base unit(or repeating unit) of the carbohydrate and/or the polyvinyl alcohol, bis a value of the amount (g) of the carbohydrate and/or the polyvinylalcohol used divided by the formula weight of the base unit thereof andc is the number of moles of the metallic halide (in the case of themethod (i), c of the relationship [I] represents the number of moles ofthe metallic halide used in the reaction thereof with ammonia).

For instance, in the above-mentioned relationship [I], in the case whereglucose is used as carbohydrate, a of the relationship [I] is 5, b isthe value of the amount (gr.) of the used glucose divided by theformular weight of the glucose (i.e. 180), and, in the case wherepolymerization derivative of the glucose is used as starch, a of therelationship [I] is 6 and b is the value of the amount (gr.) of the usedstarch divided by the formular weight of the base unit of the starch(i.e. 324).

As the value N of the above-mentioned relationship [I] is decreased, theproportion of the metallic nitride contained in the produced metalliccarbonitride increases. Therefore, according to the present invention, ametallic carbonitride having any desired composition can be effectivelyproduced.

According to the present invention, the precursor obtained in theabove-mentioned methods (i) or (ii) is then calcined in the subsequentstep. Thus, the precursor is pyrolytically decomposed to convert theinorganic substance and the desired metallic carbonitride is obtained.

The calcination temperature is generally within the range of from 700°C. to 2300° C., preferably from 800° C. to 2000° C. The precursor ispreferably heated up to about 400° C. at a heating rate of from about0.1 to about 10° C./min. In the case of the heating rate being too fast,the calcination operation becomes difficult due to the swelling of theprecursor. On the other hand, in the case of the heating rate being tooslow, it is likely that the particle size of the resultant metalliccarbonitride becomes undesirably large. After the precursor is heated toabout 400° C., the precursor can be rapidly heated to a desiredcalcination temperature. The calcination is preferably carried out, inthe absence of water and oxygen, in a gas atmosphere of argon, helium,hydrogen or ammonia or in vacuo. The calcination period of time isgenerally within the range of from 0.5 to 10 hours, preferably 1 to 3hours.

The present invention now will be further illustrated by, but is by nomeans limited to, the following Examples. In the following Examples, thecompositions of the calcined products were identified according to aX-ray diffraction analysis and the specific surface areas of themetallic carbonitrides were determined according to a BET method basedon nitrogen gas adsorption.

EXAMPLE 1

A quartz reaction tube having an inner diameter of 4 cm and a length of40 cm and provided with a gas feed pipe, a gas discharge pipe, anagitator and a dropping funnel was used and the atmosphere therein wasreplaced with argon. A solution of 12.0 g of titanium tetrachloridedissolved in 150 ml of toluene was then introduced into the reactiontube. The reaction tube was dipped in a dry ice-methanol bath andgaseous ammonia was continuously blown through the gas feed pipe intothe titanium tetrachloride in toluene solution with stirring for 60minutes at a rate of 50 m mol/min. Upon the blowing of the gaseousammonia, orange precipitate of the reaction product was formed.

After removing the dry ice-methanol bath from the reaction tube, thereaction mixture is heated to a temperature of 25° C., while argon isgently passed through the reaction tube. Thereafter, a suspension of 7.0g of saccharose in 30 ml of toluene was added, through the droppingfunnel, to the reaction mixture for 10 minutes. Upon the addition of thesaccharose, the orange precipitate was changed to a reddish-brownprecipitate.

After the toluene was distilled off, the precursor was first heated to450° C. at a heating rate of 3° C./min and, then, heated to 700° C. at aheating rate of 5° C./min, while argon was gently passed through thereaction tube. Thereafter, the precursor was maintained at a temperatureof 1400° C. for 2 hours under an argon atmosphere in an electricfurnace. Thus, 3.2 g of titanium carbonitride in the form of finelydivided powder was obtained. The resultant titanium carbonitride was asolid solution of 83% by weight of titanium carbide and 17% by weight oftitanium nitride. The nitrogen content of the resultant product was 3.8%by weight as measured by a Kjeldahl analysis. The specific surface areaof the titanium carbonitride was 3.6 m² /g and the finely dividedparticles had a diameter of from 0.1 to 0.5 microns as visuallydetermined by a scanning type electron microscope.

EXAMPLE 2

Example 1 was repeated, except that the amount of the saccharose waschanged to 3.4 g. Thus, 3.1 g of titanium carbonitride in the form offinely divided powder was obtained. This titanium carbonitride was asolid solution of 37% by weight of titanium carbide and 63% by weight oftitanium nitride. The specific surface area of the product was 3.8 m²/g.

EXAMPLE 3

Example 1 was repeated, except that 11.0 g of silicon tetrachloride wasused instead of the titanium tetrachloride. Thus, 2.3 g of siliconcarbonitride in the form of finely divided powder was obtained. Thissilicon carbonitride was a mixture of 78% by weight of silicon carbideand 22% by weight of silicon nitride. The specific surface area of theproduct was 4.1 m² /g.

EXAMPLE 4

Example 1 was repeated except that 14.0 g of vanadium tetrachloride wasused instead of the titanium tetrachloride and that the amount of thesaccharose was changed to 8.0 g. Thus, 4.3 g of vanadium carbonitride inthe form of finely divided powder was obtained. This vanadiumcarbonitride was a solid solution of 78% by weight of vanadium carbideand 22% by weight of vanadium nitride. The specific surface area of theproduct was 2.5 m² /g.

EXAMPLE 5

Example 1 was repeated, except that 5.0 g of tungsten hexachloride wasused instead of the titanium tetrachloride and that the amount of thesaccharose was changed to 1.6 g. Thus, 2.4 g of tungsten carbonitride inthe form of finely divided powder was obtained. In this Experiment, thetungsten hexachloride, as a suspension in toluene, was reacted withammonia. The tungsten carbonitride thus obtained was a mixture of 79% byweight of tungsten carbide and 21% by weight of tungsten nitride. Thespecific surface area of the product was 0.9 m² /g.

EXAMPLE 6

Example 1 was repeated except that 8.8 g of starch was used instead ofsaccharose. Thus, 3.4 g of titanium carbonitride in the form of a finelydivided powder was obtained. This was a solid solution of 66% by weightof titanium carbide and 34% by weight of titanium nitride. The specificsurface area of the product was 3.1 m² /g.

EXAMPLE 7

Example 1 was repeated, except that 2.8 g of polyvinyl alcohol(saponification degree: 100%) was used instead of saccharose. Thus, 3.0g of titanium carbonitride in the form of finely divided powder wasobtained. This was a solid solution of 81% by weight of titanium carbideand 19% by weight of titanium nitride. The specific surface area of theproduct was 2.9 m² /g.

EXAMPLE 8

Example 1 was repeated, except that 7.6 g of galactose was used insteadof the saccharose. Thus, 3.4 g of titanium carbonitride in the form offinely divided powder was obtained. This titanium carbonitride was asolid solution of 92% by weight of titanium carbide and 8% by weight oftitanium nitride. The specific surface area of the product was 3.4 m²/g.

EXAMPLE 9

After the air contained in the reaction tube as used in Example 1 wasreplaced with argon, a solution of 12.0 g of titanium tetrachloridedissolved in 150 ml of toluene was introduced into the reaction tube. Asuspension of 7.1 g of saccharose in 30 ml of toluene was, then,dropwise added, with stirring, to the toluene solution of titaniumtetrachloride at a temperature of 25° C. for 10 minutes. Thereafter, thereaction tube was dipped in a dry ice-methanol bath and 50 m mol/min. ofgaseous ammonia was blown, with stirring, through the reaction mixturefrom a gas feed pipe for 60 minutes.

After the toluene was distilled off, the precursor thus obtained wascalcined in a manner as described in Example 1, except that gaseousammonia was used up to 700° C. and argon was used after 700° C. Thus,3.3 g of titanium carbonitride in the form of finely divided powder wasobtained. This titanium carbonitride was a solid solution of 84% byweight of titanium carbide and 16% by weight of titanium nitride. Thespecific surface area of the product was 4.3 m² /g.

EXAMPLE 10

Example 9 was repeated, except that 3.2 g of tantalum pentachloride wasused instead of titanium tetrachloride and that the amount of thesaccharose was changed to 1.5 g. 1.6 g of tantalum carbonitride in theform of finely divided powder was obtained. This tantalum carbonitridewas a solid solution of 88% by weight of tantalum carbide and 12% byweight of tantalum nitride. The specific surface area of the product was10.5 m² /g.

We claim:
 1. A process for producing a metallic carbonitride said metalbeing selected from the group consisting of Groups IV, V and VI of thePeriodic Table of Elements, comprising the step of calcining a precursorobtained by (i) reacting the reaction product of ammonia and the halideof a metal with at least one member selected from the group consistingof carbohydrates and polyvinyl alcohols, or (ii) the reaction product ofthe halide of a metal and at least one member selected from the groupconsisting of carbohydrates and polyvinyl alcohols with ammonia.
 2. Aprocess as claimed in claim 1, wherein said carbohydrates are selectedfrom monosaccharide, oligosaccharide and polysaccharide.
 3. A process asclaimed in claim 1, wherein said carbohydrates are selected from thegroup consisting of glucose, galactose, arabinose, saccharose, maltose,lactose, starch and cellulose.
 4. A process as claimed in claim 1,wherein said polyvinyl alcohols are saponified polyvinyl acetates inwhich 30 to 100% of acetyl group is saponified.
 5. A process as claimedin claim 1, wherein the amount of the carbohydrate and/or the polyvinylalcohol is within the range of the value N defined by the followingrelationship of from more than 0 to less than
 6.

    N=(a×b)/c

wherein a is the number of hydroxyl groups contained in the base unit ofthe carbohydrate and/or the polyvinyl alcohol, b is the value of theamount (g) of the carbohydrate and/or the polyvinyl alcohol used dividedby the formula weight of the base unit thereof and c is the number ofmoles of the metallic halide.
 6. A process as claimed in claim 5,wherein said value N is within the range of from more than 0 to lessthan
 4. 7. A process as claimed in claim 1, wherein the calcination ofthe precursor is carried out at a temperature of from 700° to 2300° C.8. A process as claimed in claim 7, wherein the calcination temperatureis within the range of from 800° to 2000° C.
 9. A process as claimed inclaim 7, wherein the precursor is heated to a temperature of at leastabout 400° C. at a heating rate of 0.1 to 10° C./min.
 10. A process asclaimed in claim 1, wherein said halide of the metal is selected fromthe group consisting of the chlorides of silicon, titanium, vanadium,tantalum and tungsten.
 11. A process as claimed in claim 1, wherein saidreaction product of the ammonia and the halide of the metal is preparedby gradually adding liquid ammonia to or blowing gaseous ammonia througha solution or suspension of the halide of the metal in an inert organicsolvent at a temperature of from -80° to 300° C.
 12. A process asclaimed in claim 11, wherein said reaction product is reacted with atleast one member selected from the group consisting of the carbohydratesand the polyvinyl alcohols at a temperature of from -50° to 150° C. 13.A process as claimed in claim 1, wherein said reaction product of atleast one member selected from the group consisting of the carbohydratesand the polyvinyl alcohols and the halide of the metal is prepared byadding at least one member selected from the group consisting of thecarbon hydrates and the polyvinyl alcohol or a solution or suspensionthereof in an inert organic solvent to a solution or suspension of thehalide of the metal in an inert organic solvent at a temperature of from-50° C. to 150° C.
 14. A process as claimed in claim 1, wherein saidreaction product of at least one member selected from the groupconsisting of the carbohydrates and the polyvinyl alcohol and the halideof the metal is prepared by adding a solution or suspension of thehalide of the metal in an inert organic solvent to at least one memberselected from the group consisting of the carbohydrates and thepolyvinyl alcohol or a solution or suspension thereof in an inertorganic solvent at a temperature of from -50° to 150° C.
 15. A processas claimed in claim 12 or 13, wherein said reaction product is reactedwith liquid or gaseous ammonia at a temperature of from -80° to 300° C.